You can actually see that switch by looking at the areas of the brain that respond to scratching. In a study that looked at people scratching their itches in an fMRI machine, researchers noticed that while there wasn't any one identifiable "itch center" in the brain, scratching seemed to activate parts of the brain that are strongly associated with pleasure, reward, and craving. Of course, scratching also feels good because it works: It temporarily disrupts the unpleasant itch sensation.
To understand why, you have to know a little about the yin and yang of itch and pain. Until recently, itch was considered nothing more than a subset of pain—a sort of "pain lite" caused by low-level activation of pain neurons. But while the two sensations do share many of the same nervous system pathways, new research has shown that itch has its own dedicated nerve cells, molecules, and cellular receptors. There's crosstalk. Those interactions are what Zhou-Feng Chen , a developmental biologist and the director of Washington University's Center for the Study of Itch , wanted to better understand back in Their work led to the discovery of the first "itch gene," GRPR gastrin-releasing peptide receptor , which seemed to be key in relaying itch signals and only itch signals from the spine to the brain.
Chen's research group took a batch of genetically altered mice without the GRPR gene, and then they made them itch. For instance, a wooden table can have a scratch. Scratch as a verb is generally transitive. As a verb it generally means to either tend to an itch by rubbing and scraping with your fingernails, or it can mean to cause or create scratches.
In casual speech, people often substitute the verb itch for the verb scratch. If you use itch in the place of scratch in a casual conversation, everyone will understand what you mean.
Feedback Tired of Typos? Word of the Day. Meanings Meanings. This interference happens because, while scratching, nerve cells in the spinal cord carry pain signals to the brain instead of itch signals. Chen and team found that serotonin has a muddling effect on the sensation of pain and itch, whereby, as serotonin spreads from brain to spinal cord, pain-sensing neurons instead influence itch intensity.
Based on our own experiences of chronic eczema , Medical News Today asked Dr. The reason is that, at least from our studies in mice, when you scratch to create pain, the brain in response begins to produce more serotonin to inhibit pain the brain does not want to have pain in your body.
What we found is that while serotonin inhibits itch, it also can activate the itch receptor and make more itching. The researchers bred mice that lacked the genes necessary for serotonin production.
When the serotonin-free mice were injected with a substance that would normally cause itching, the researchers found that the mice did not scratch as much as a control group of mice with the serotonin-producing genes.
Next, the mice that lacked the serotonin genes were injected with serotonin. The injected serotonin caused the mice to scratch in a manner that was consistent with the control group. The team considered different approaches that might be useful in minimizing the itching sensation. They ruled out suppressing serotonin as — although this made the mice less sensitive to itching — serotonin is too valuable a chemical in the body. Growth, aging, bone metabolism, mood and pain are all regulated by serotonin, so blocking this neurotransmitter would have consequences throughout the body.
Instead, the team focused their attention on disrupting communication between serotonin and the nerve cells in the spinal cord that relay the itching impulse from brain to skin.
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